Focused and directed laser beams are commonly used for a variety of processes, such as drilling of blind, through and micro-vias, laser imaging, dicing of substrates and modification or customization of integrated circuits, drilling, cutting, and selective material removal and other complex machining and micro-machining operations involving materials such as thin metals, polymers, integrated circuits and substrates. Certain such processes are referred to as “focal point machining”, wherein the object is generally to focus and concentrate the energy of one or more laser beans to converge at a desired spot, or as “laser imaging”, wherein the objective is to image an apertured area of a laser beam onto the surface of an object. Such processes have become very complex, often involving the concurrent or sequential of use of single or multiple lasers or multiple types of lasers, such as visible, infra-red (IR) and ultraviolet (UV) lasers, in concurrent or sequential operations.
Such processes, however, are faced with a number of recurring and related problems. For example, a given operation, such as the drilling of a via or the micro-machining of an integrated circuit or a machine part often requires only a part of the power of a laser beam, so that much of the power of a laser is underutilized. This problem is related to still another problem, which is the time required to perform operations on a given workpiece. That is, many of the processes employing lasers, such as drilling vias in a circuit board, substrate or integrated circuit or performing machining operations on a integrated circuit or mechanical part require a very large number of operations and a correspondingly long time to complete a given workpiece.
The general solution to both problems is well known and understood, however, and includes method for splitting a single laser beam into multiple sub-beams, or beamlets, which are typically used concurrently to perform multiple, identical operations in parallel.
In a typical laser process system of the prior art employing these methods, a source beam generated by a laser is passed through one or more splitter stages, each of which includes a splitter which divides a single source beam into two or more beamlets, and a collimating prism associated with each splitter which directs and focuses the beamlets from the splitter into a group of parallel beamlets. The splitting and collimating process may be repeated sequentially to generate the desired number of beamlets in each group, and the desired number of groups of beamlets. Each group of beamlets then passes through a “path equalizer”, each of which is comprised of a transmission path through multiple galvanometer controlled mirrors arranged and controlled to equalize the length that each beamlet traverses in reaching the target, or workpiece. A final pair of steerable mirrors for each group of beamlets and a scan lens shared among the groups of beamlets then permits the groups of parallel beamlets to be “steered” and focused in parallel onto a desired target area of the workpiece. Lastly, the equalization paths may include “beam dumps” whereby each group of parallel beamlets may be steered so that one or more beamlets of a group are intercepted by a mask or absorbing element and thereby “dumped”, or eliminated, from the group.
While these methods are in common use, a continuing problem with such systems, for example, is that while the steerable mirrors in the beam transmission paths generally permit each group of beamlets to be steered independently of the other groups, the pattern of beamlets within each group are generally constrained to such fixed patterns of parallel beamlets as may be generated by one or more splitter stages. That is, and although the spacing between beamlets in a group can be controlled to a degree by the steerable mirrors in the transmission path and although some beamlets may be eliminated from a group by steering them into a beam dump, the beamlets within a group may not be individually steered to desired targets.
As such, and unless the pattern of targets, such as a layout of vias to be drilled, coincides with the available patterns of beamlets in a group, it will be necessary to eliminate at least some beamlets from a group, by beam dumping, for example, to avoid drilling unwanted vias. As a consequence, a significant portion of the efficiency of the system as regards usage of the available laser power may be negated by the need to “dump” a significant portion of the beamlets. Also, the time required to process a workpiece may increase significantly due to the reduction in the number of beamlets available in each work step and the consequent increase in the required number of work steps.